Well in the new Blu-Ray Trilogy (Edit: Complete Saga... I always forget there are 6 SW movies, not 3 xD) box, there is an interview to Uncle George about the premature death of Obi-Wan. Lucas says that in his first draft of the Star Wars Universe story, Yoda didn't exist. There was only one Jedi left, and he was Obi. Then he starts recalling that in his original story, only ONE Death Star was constructed and destroyed, and Kenobi died only at the end (exactly at the point of ROTJ when Yoda dies). So he had to concentrate almost everything in one movie, due to the lack of money and the uncertain future of his project (he thought the movie would have been a flop, with no sequels). This explains why we have TWO Death Stars, and TWO Jedi masters (both dying before the end of the story arc), because at the time of ESB, there was no more Jedi Master, but there was an Initiate (Luke), so he created Yoda. Even the Emperor was supposed to be a politician and a puppet, ruled by the Moffs (like Tarkin). But then success... A sequel... The MONEY! xD It changed the story...
So, Obi-Wan's death can be seen like it was intentional, unintentional, emotional... Everything. It is what we think it is, because initially there was no intent in making him return (In an early draft of the script, Kenobi was even Owen Lars' eldest brother, and in fact, Luke's real uncle). :P
(And here comes the OT geek rant: Qui Gon had the same ability as Obi-Wan, because -HE TAUGHT OBI- how to become one with the force, so why at the end of ROTJ Anakin appears as one with the force, and Qui Gon doesn't? It would've had much sense to add Neeson over Shaw, than Christensen! And here come out the millions plot holes typical of the Prequels...)